Motorized vehicles include a power plant (e.g., combustion engine, or electric motor) that produces driving power. The driving power is transferred through a transmission to a driveline for driving a set of wheels at selected gear ratios. As is well known, automatic transmissions shift automatically to the appropriate gear ratio based on various vehicle operating conditions including speed and torque. Typically, a desired transmission operating mode or range is selected by the vehicle operator. The ranges provided by most automatic transmissions generally include Park, Neutral, Reverse and Drive. In Drive, the automatic transmission automatically shifts between two or more different forward gear ratios based on the vehicle operating conditions.
Traditionally, a driver interface device is provided which the vehicle operator shifts to select the desired transmission range. The driver interface device is linked to the automatic transmission by a range shift mechanism which typically includes a series of interconnected mechanical devices such as levers, push/pull rods, cables and the like. The number and size of such mechanical components make it difficult to package the range shift mechanism between the driver interface device and the transmission and can add significant frictional resistance to the overall system. As a result, the overall cost for design, manufacture and assembly of the vehicle is increased. In an attempt to address such issues related to mechanically-shifted transmission range shift mechanisms, several “shift-by-wire” range shift mechanisms have been developed.
At least one shift-by-wire range shift mechanism controls the operation of the transmission between a park and out-of-park mode using an electronically controlled solenoid valve operable to enable a flow of pressurized fluid within the transmission. The pressurized fluid operates a series of fluid control valves and a hydraulic servo valve assembly that shifts the transmission through a mechanical linkage system. Such a system may exhibit slow valve actuation at low transmission fluid temperatures. At fluid temperatures below around −10° C., high transmission fluid viscosity inhibits valve movement, slowing the range shift mechanism. Accordingly, an electronic transmission range select system with improved response time for shifting the transmission between a park and out-of-park mode is desired.